On a serious note I think that male homosexuals are highlighted for one simple reason. Fear. It really is homophobia in men. Lesbians pose no threat because they don't want to do anything to us. If anything, that just makes us want to try harder to have sex with them. They are still women afterall, we'll want to have sex with them no matter which way they swing. That, and the possibility of a three way always exists.
Male homosexuals on the other hand could possiby want to put something up our bum. Not that many male homosexuals would want to since straight guys tend to be pretty skanky. But the possibility exists. Personally, any day in which I do not get stabbed, shot, have something up my butt or really have any foriegn object enter my body (splinters included) in any manner is considered a success.
For the straight guys out there picture this. Your standing in line when a large man gets behind you. He brushes up against you and you can feel the stubble from his chin on your neck. He puts one large hand on your hip and the other in your pocket. In a deep husky voice he whispers "Those pants would look great on my floor." If imagining that didn't make your skin crawl, then you're probabbly gay. If that had been described as a woman and she said "My girlfriend and I think you should come back to our place." you'd already have your fly halfway undone.